| 1. |
- Lagerwall, J. P. F., et al.
(författare)
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Chiral smectic C subphases induced by mixing a bistereogenic antiferroelectric liquid crystal with a non-chiral liquid crystal
- 2005
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Ingår i: Ferroelectrics. - : Informa UK Limited. - 0015-0193 .- 1563-5112. ; 315, s. 221-230
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Tidskriftsartikel (refereegranskat)abstract
- By mixing a bistereogenic antiferroelectric liquid crystal (AFLC) compound, exhibiting only the SmQ* and SmC a * mesophases, with the achiral N-SmC liquid crystal HOAB we could induce all three AFLC SmC-type subphases, SmC α *, SmC β * and SmC γ *. This seems to be in contradiction with two recent postulations regarding the subphase stability, one of which suggests that the subphases appear as a result of strong chiral interactions, the other that these phases require high smectic order, something one would generally not expect in mixtures. We have studied the helical pitch, optical tilt angle, spontaneous polarization and the x-ray diffraction due to the smectic layering, as a function of mixing ratio in order to better understand the relation between phase sequence and mixture composition. The smectic layer spacing shows a strongly non-linear behavior, suggesting that the basic structure of the pure AFLC substance is retained up to a HOAB content of about 75%.
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| 2. |
- Liang, H. L., et al.
(författare)
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Tuning the defect configurations in nematic and smectic liquid crystalline shells
- 2013
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Ingår i: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. - : The Royal Society. - 1364-503X .- 1471-2962. ; 371:1988
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Tidskriftsartikel (refereegranskat)abstract
- Thin liquid crystalline shells surrounding and surrounded by aqueous phases can be conveniently produced using a nested capillary microfluidic system, as was first demonstrated by Fernandez-Nieves et al. in 2007. By choosing particular combinations of stabilizers in the internal and external phases, different types of alignment, uniform or hybrid, can be ensured within the shell. Here, we investigate shells in the nematic and smectic phases under varying boundary conditions, focusing in particular on textural transformations during phase transitions, on the interaction between topological defects in the director field and inclusions in the liquid crystal (LC), and on the possibility to relocate defects within the shell by rotating the shell in the gravitational field. We demonstrate that inclusions in a shell can seed defects that cannot form in a pristine shell, adding a further means of tuning the defect configuration, and that shells in which the internal aqueous phase is not density matched with the LC will gently rearrange the internal structure upon a rotation that changes the influence of gravity. Because the defects can act as anchor points for added linker molecules, allowing self-assembly of adjacent shells, the various arrangements of defects developing in these shells and the possibility of tuning the result by modifying boundary conditions, LC phase, thickness and diameter of the shell or applying external forces make this new LC configuration very attractive.
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| 3. |
- Licen, M., et al.
(författare)
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Correlation between structural properties and iridescent colors of cellulose nanocrystalline films
- 2016
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 23:6, s. 3601-3609
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the effect of shear flow applied during the drying of aqueous suspension of cellulose nanocrystals on optical reflective properties and structural characteristics of the resulting solidified films. Shear flow can significantly improve internal structural homogeneity of the films, while its effect on optical reflective properties is relatively minor. The measured width of the selective reflection peak is an order of magnitude larger than expected for an ideal helically modulated structure, which reflects a distribution of pitch values and possibly also of regimes of distorted helical modulation. We attribute these imperfections to the broad size distribution of the cellulose nanocrystals.
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| 4. |
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| 5. |
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| 6. |
- Caillaud, B., et al.
(författare)
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Safe and ergonomic welding masks by fast liquid crystals
- 2008
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Ingår i: Molecular Crystals and Liquid Crystals. - : Informa UK Limited. - 1563-5287 .- 1542-1406. ; 494, s. 195-204
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Tidskriftsartikel (refereegranskat)abstract
- Recent developments in welding technology, in particular the high intensity pulsed welding arc, have sharpened the requirements on speed and adjustable attenuation for safe and ergonomic operations. With this advent the conventional welding helmets based on nematic liquid crystals are facing difficulties because the nematics are not responding fast enough to stroboscopically follow the changing intensity of the arc during pulsed welding. We propose here a new generation of welding shutters based on smectic (ferroelectric or antiferroelectric) liquid crystals which are fast enough to be synchronized to follow pulsed arc regimes and hence permitting a better visibility of the object under work. The two varieties of smectic materials used are polymer-stabilized in order to make the device shock-proof, to prevent the formation of specific defects such as stripes and chevrons, and to reduce the back-relaxation time in the antiferroelectric case.
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| 7. |
- Lagerwall, J. P. F., et al.
(författare)
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Vätskekristallin mjuk materia
- 2009
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Ingår i: Fysikaktuellt. ; :3, s. 18-19
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 8. |
- Liang, H. L., et al.
(författare)
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Nematic-Smectic Transition under Confinement in Liquid Crystalline Colloidal Shells
- 2011
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 106:24
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Tidskriftsartikel (refereegranskat)abstract
- We carry out the first study of smectic liquid crystalline colloidal shells and investigate how their complex internal structure depends on the director configuration in the nematic phase, preceding the smectic phase on cooling. Differences in the free energy cost of director bend and splay give an initial skewed distribution of topological defects in the nematic phase. In the smectic phase, the topological and geometrical constraints of the spherical shell imposed on the developing 1D quasi-long-range order create a conflict that triggers a series of buckling instabilities. Two different characteristic defect patterns arise, one driven by the curvature of the shell, the other by the strong nonuniformities in the director field in the vicinity of the topological defects.
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| 9. |
- Liang, H. L., et al.
(författare)
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Towards tunable defect arrangements in smectic liquid crystal shells utilizing the nematic-smectic transition in hybrid-aligned geometries
- 2012
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 8:20, s. 5443-5450
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Tidskriftsartikel (refereegranskat)abstract
- We produce and investigate liquid crystal shells with hybrid alignment-planar at one boundary, homeotropic at the other-undergoing a transition between the nematic (N) and smectic-A (SmA) phases. The shells display a dynamic sequence of patterns, the details depending on the alignment agents and on the diameter and thickness of the shell. In shells of sufficient diameter we typically find a transient striped texture near the N-SmA transition, stabilising into a pattern of tiled, more or less regularly spaced focal conic domains in the SmA phase. The domain size and spacing decrease with reduced shell thickness. In case of strong homeotropic anchoring at one boundary and small shell size, however, the increased curvature favors homeotropic against planar alignment in the smectic phase, and the shell then tends to adapt to complete homeotropic alignment at the final stage of the transition. This is the first study of hybrid-aligned smectic shells and the results constitute a beautiful demonstration of the capacity for dynamic structure formation and reformation via self-assembly in soft matter. The new patterns extend the range of arrays of topological defects that can be realised with liquid crystals in spherical morphology and the correlation between the feature arrangements and the variable parameters of the shell and its environment opens a route towards tunability. However, the observed strong impact from increasing curvature, even for these rather large shells, indicates that the choice of alignment agents inducing planar or homeotropic alignment with varying strength will become critical when targeting the most attractive colloidal size scale of about a micron or smaller.
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| 10. |
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| 11. |
- Trollsås, M., et al.
(författare)
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The influence of the molecular structure on the second-order nonlinear optical properties of pyroelectric liquid crystalline polymers
- 1998
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Ingår i: American Chemical Society Symposium Series (ACS). - Washington, DC : American Chemical Society. - 0097-6156 .- 1947-5918. ; 695, s. 315-327
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Tidskriftsartikel (refereegranskat)abstract
- Pyroelectric Liquid Crystal Polymers (PLCP), a novel class of material with intrinsic polar order developed in our laboratory, are discussed. Thin films (2-4µm) of PLCP were prepared by photopolymerization of ferroelectric liquid crystalline monomers in the chiral smectic C (SmC*) phase. The poly(acrylate) materials have been structurally modified in order to improve their nonlinear optical and thermal properties. Further are their longterm nonlinear optical properties discussed based on results from second harmonic generation (SHG), spontaneous polarization (Ps), and dielectric spectroscopy.
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